Recording apparatus

ABSTRACT

A recording apparatus locates a photo detector at a predetermined position on an optical base, stopping the rotation of a resist master disk, activating a focusing laser, and optimally positioning a head by means of a head slider control circuit. The resist master disk then starts to rotate, followed by the starting of a focus servo circuit. A focus fine adjust circuit effects a fine movement of the photo detector using positioning data to achieve optimum focusing. A differential amplifier serves to cause a recording lens to adjust to nullify the error signal. Display information is compared with the focusing position data and, when the numerical information coincides with the focusing position data, the above-mentioned focusing data is used as optimum focusing position data for the initial setting of the optimum focusing position. The use of optimum focusing position data in the form of numerical values permits easy initial setting of the optimum focusing position for different types of resist master disks.

TECHNICAL FIELD

The present invention relates to an improvement in a laser cuttingmachine (referred to as a “recording apparatus”, hereinafter).

BACKGROUND ART

A recording apparatus has been known which has, as shown in FIG. 1, arecording laser 1 and a focusing laser 3. In operation of this recordingapparatus, initial setting of optimum focusing position of a recordinglens 21 is performed in accordance with the following procedure. As thefirst step, a head 19 is positioned at an optimum position by means of ahead positioning mechanism 17, while a resist master disk 20 is notrotating. Then, the master disk 20 is driven to rotate at apredetermined speed and, when the disk rotation has become steady atthat speed, the recording laser 1 is activated so that recording laserlight is made to be incident to the master disk 20 via mirrors 5, 7 and9 and then through a recording lens 21. The laser light reflected by themaster disk 20 runs backward along the same optical path as the incidentlight so as to impinge upon a CCD camera 13 from the mirror 5, whereby alaser spot image is formed on the monitor 15 through the camera 13. Theoperator, while visually observing the state of the laser spot image,controls a motor driver 29 so as to control a motor 27 thereby moving aphoto-detector (PD) to the left and right. A servo circuit 31 performs afine control of the position of the recording lens in the up and downdirections so as to position the recording lens 21 at such a positionthat the above-mentioned laser light impinges upon the center of the PD23 which is set at a position as a result of the above-mentioned controlperformed by the operator. This operation is repeated so that therecording lens 21 is set at the optimum focusing position.

In the above-described operation for initially setting the recordinglens 21 at the optimum position, the laser spot image of the recordinglaser light displayed on the monitor 15 linearly changes in accordancewith the movement of the PD 23, because the laser spot light is analoginformation. Considerably high degrees of skill and experience,therefore, are required in order to adequately position the recordinglens 21 by visually finding the laser spot image corresponding to theoptimum focusing position of the recording lens 21 through continuousvisual chasing of the change in the laser spot image. The optimumfocusing position of the recording lens 21 delicately varies accordingto the type of the resist master disk. Therefore, the above-describedwork is considerably troublesome even for skilled and experiencedoperators. Thus, it is not easy to position the recording lens 21 with ahigh degree of accuracy.

The described recording apparatus suffers from another disadvantage inthat, even if the recording lens 21 has been set at the optimum focusingposition, the data indicative of such optimum focusing position cannotbe relied upon for the purpose of reproduction of the optimum focusingposition, because the data is analog data which is in the form of thelaser spot image displayed on the monitor 15 and cannot be stored.

Consequently, the above-described troublesome work is necessarilyconducted each time the type of the resist master disk is changed, thusimpairing the efficiency of the whole process.

Accordingly, an object of the present invention is to provide arecording apparatus in which the data indicative of the optimum focusingposition of the recording lens is changed into numerical values so as tofacilitate the work for initially setting the optimum focusing positionof the recording lens for each type of resist master disk.

DISCLOSURE OF THE INVENTION

To this end, the present invention provides a recording apparatus forexposing a resist master disk to a recording laser light through arecording lens which has been set at an optimum focusing position,comprising: displaceable laser light detecting means for receiving afocusing laser light which has been applied to and reflected from theresist master disk during initial setting of the optimum focusingposition, and for producing a detection signal indicative of the amountof deviation, from a predetermined light receiving position, of thelight receiving position where the reflected focusing laser light isreceived; servo means responsive to the detection signal so as toautomatically adjust the relative position of the recording lens withrespect to the resist master disk in such a manner as to eliminate thedeviation, thereby setting the recording lens at the optimum focusingposition; displacement amount detecting means for detecting the amountof displacement of the laser light detecting means; and display meansfor changing the output from the displacement amount detecting meansinto numerical values and displaying the numerical values.

According to the features of the recording apparatus set forth above,the amount of displacement of the laser light detecting means acquiredin the course of an initial setting performed by a skilled operator ischanged into a numerical value which can be relied upon in the nextinitial setting of the optimum focusing position. The next initialsetting, therefore, can easily be conducted even by an operator who isnot so skilled. By holding the numerical optimum focusing position datafor each of a plurality of types of resist master disks, initial settingof the optimum focusing position can easily be executed each time adifferent type of resist master disk is used, thus achieving a furtherimprovement in the efficiency of the whole process.

Preferably, the recording apparatus in accordance with the presentinvention further comprises: reference displacement amount setting meansin which a reference displacement amount has been set in terms of theamount of the displacement required to obtain coincidence between thelight receiving position at which the focusing laser light is receivedand the reference light receiving position under such a condition thatthe recording lens has been set at the optimum focusing position; andautomatic displacement amount adjusting means for automaticallyadjusting the displacement amount of the laser light detecting meanssuch that the detection output from the displacement amount detectingmeans coincides with the reference displacement amount.

Thus, a preferred form of the recording apparatus in accordance with thepresent invention has reference displacement amount setting means andautomatic displacement amount adjusting means.

The reference displacement amount setting means sets a referencedisplacement amount in terms of the amount of displacement required forachieving coincidence between the light receiving position at which thefocusing laser light is received and the reference light receivingposition under such a condition that the recording lens has been set atthe optimum focusing position. The automatic displacement amountadjusting means automatically adjusts the amount of the displacement ofthe laser light detecting means such that the detection output from thedisplacement amount detecting means coincides with the referencedisplacement amount.

In the preferred form of the present invention set forth above, theamount of displacement of the laser light detecting means isautomatically adjusted such that the detected displacement amountcoincides with the reference displacement amount. Thus, the amount ofdisplacement of the laser light detecting means can be automaticallyadjusted without troubling the operator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the whole structure of a knownrecording apparatus.

FIG. 2 is a block diagram showing the whole structure of a firstembodiment of the recording apparatus.

FIG. 3 is an illustration of the positional relationship between aphoto-detector and a spot formed by a focusing laser light.

FIG. 4 is a flow chart showing a focusing process performed in the firstembodiment of the recording apparatus.

FIG. 5 is an illustration of a focusing error detecting system using afocusing laser light for detecting the focusing error of a recordinglens.

FIG. 6 is a chart illustrative of variations of the relationship betweenthe depth and breadth of bits (or grooves) formed in a disk which isproduced by copying the resist master disk produced by the firstembodiment.

FIG. 7 is a chart illustrative of variations of the relationship betweenthe depth and breadth of bits (or grooves) formed in a disk which isproduced by copying a resist master disk produced by a known process.

FIG. 8 is a block diagram showing the whole structure of a secondembodiment of the recording apparatus.

FIG. 9 is a block diagram showing the internal structure of an optimumfocusing position confirming circuit incorporated in the apparatus shownin FIG. 8.

FIG. 10 is a flow chart showing a focusing process performed in thesecond embodiment of the recording apparatus.

Reference Numerals: 61, 63, 65 mirror 69 monitor 71 head mechanism 73focusing laser 75 head slider 77 head  77a recording lens  77b VCM 81photo-detector 85 reduction gear mechanism 87 potentiometer 93 digitaldisplay unit 95 motor 97 motor driver circuit 99 focus fine adjustingcircuit 101  head slider control circuit 103  focus servo circuit  103a differential amplifier 105  optimum focusing position confirming circuit107  manual switch 110  resist master disk

THE BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings.

FIG. 2 is a block diagram showing the whole structure of a firstembodiment of the recording apparatus.

As will be seen from this Figure, the recording apparatus has an opticalsystem 50 and a focus servo system 80 which causes a recording lens 77 aof the optical system 50 to follow up a resist master disk 110 with anaccuracy on the order of sub-microns. The recording apparatus furtherhas a shifting mechanism (not shown) which drives the resist master disk110 at a high degree of rotational recision and causes a relativemovement between the resist master disk 110 and the optical system 50,as well as a signal processing circuit (not shown) which includescircuits such as a modem circuit which performs modulation anddemodulation of a signal indicative of the recorded information.

The optical system 50 includes a recording laser 51, a power controller53, a mirror 55, a modulator 57, mirrors 59 to 65, a CCD camera 67, amonitor 69, a head mechanism 71 and a focusing laser 73.

The focus servo system 80 includes a photo-detector (PD) 81, a reductiongear mechanism 85, a potentiometer 87, an amplifier 89, an A/D converter91, and a digital display unit 93. The focus servo system 80 further hasa motor 95, a motor drive circuit 97, a focus fine adjusting circuit 99,a head slider control circuit 101, and a focus servo circuit 103.

The above-described components of the optical system 50, as well as thePD 81, potentiometer 87 and the motor 95 which are components of thefocus servo system 80, are disposed on predetermined positions of asingle optical base (not shown). As will be seen from the Figure, the PD81 is movable to the left and right on the optical base.

A description will now be given of each of the components of the opticalsystem 50.

The recording laser 51 functions as a source of recording light and alsoas a source of control signal light. The recording laser 51 is, forexample, a He—Cd laser which emits the laser light of a wavelength λ(λ=441.6 nm) as the recording laser light. The power controller 53directs the laser light coming from the recording laser 51 to the mirror55 and controls the intensity of the laser light from the recordinglaser 51 upon receipt of a detection signal from a photo-detector (notshown) for detecting a portion of the laser light which runs straightafter being transmitted through the mirror 55. The modulator 57 may be,for example, an acoustic optical effect (A/O) light modulator which usesthe correlation between acoustic wave and light wave propagated througha medium. The modulator 57 receives the laser light which has beenemitted from the recording laser 51 through the power controller 53 andguided by the mirror 55, and modulates the received laser light inaccordance with the information signals to be recorded and in accordancewith a control signal. The modulated laser light is emitted to themirror 59.

The recording laser light coming from the modulator 57 is made to beincident to the resist master disk 110 via the dichroic mirror 61,mirror 63 and a recording lens 77 a of the head mechanism 71. Therecording laser light reflected by the resist master disk 110 runsbackward along the same light path as that of the incident laser light.The mirror 59 also serves to guide this reflected laser light to the CCDcamera 67. In this embodiment, a polarization beam splitter (PBS) isused as the mirror 59.

The head mechanism 71 has a head 77 and a head slider 75 which holds thehead 77 in such a manner that the head 77 is slidable downward from ahome position which is about 30 mm spaced apart from the resist masterdisk 110.

More specifically, the head slider 75 under the control of the headslider control circuit 101 causes the head 77 to slide up and down overa stroke of several tens of millimeters with the upper stroke end set tothe above-mentioned home position. The head slider 75, when the resistmaster disk 110 is not rotating, sets the head 77 at a position wherethe recording lens 77 a can be adjusted to a “just focus” position.(This position of the head 77 is referred to as an “optimum position” ofthe head 77). The head position where the recording lens 77 a (referredto as “optimum focusing position”) is at the “just focus” position (thisposition will be referred to as an “optimum focusing position”) maydeviate from the optimum position of the head 77 by amounts which are onthe order of several μm, due to waving of the surface of the resistmaster disk 110 due to rotation of the same. However, the head slider 75is incapable of performing any control which would follow up andcompensate for this variation of the head position, because it hasinferior response characteristic.

The head 77 has the recording lens 77 a and a voice coil motor (VCM) 77b which surrounds the recording lens 77 a and which is capable of movingthe recording lens 77 a up and down over a stroke of 50 μm within thebody of the head.

A stop aperture lens having a numerical aperture NA of 0.9 isconveniently used as the recording lens 77 a. In this case, the focaldepth h (h=λ/(NA)) is very small. When the recording laser light isapplied, therefore, it is necessary that the position of the recordinglens 77 a is so adjusted that the surface of the resist master disk 110to be exposed is disposed within the focal depth h.

The VCM 77 b operates under the control of the focus servo circuit 103so as to adjust, after the head 77 has been set to the optimum positionof the head 77, the relative position of the recording lens 77 a in thehead body so as to set the recording lens 77 at the optimum focusingposition, by following up any variation of the optimum focusing positiondue to waving of the surface of the resist master disk 110 duringrotation of the disk 110.

The focusing laser 73 functions as a source of error detecting lightwhich is used in the focusing operation. For instance, a He—Ne laserwhich is capable of emitting a laser light of a wavelength of λ=632.8 nmis used as the focusing laser 73. The laser light emitted from thefocusing laser 73 is reflected by the mirror 65 and is guided to theresist master disk 110 via the dichroic mirror 61, mirror 63 and therecording lens 77 a. The laser light reflected by the resist master disk110 is guided back to the mirror 65 via the recording lens 77 a, mirror63 and the dichroic mirror 61. The mirror 65 transmits only thereflected laser light which serves as the focusing laser light, whilereflecting the reflected laser light which serves as the recording laserlight. Consequently, only the focusing laser light reflected from theresist master disk 110 is allowed to reach the photo-detector (PD) 81which is a component of the focus servo system 80. In this embodiment, apolarization beam splitter (PBS) is used as the mirror 65, as is thecase of the aforesaid mirror 59.

The CCD camera 67 generates electrical signals indicative of the spotimage formed by the recording laser light which is incident to the CCDcamera 67 through the mirror 59, and delivers the electrical signals tothe monitor 69, whereby the spot image is displayed on the monitor 69for visual observation by the operator.

A description will now be given of the components of the focus servosystem 80.

The PD 81 is a linear position detecting sensor or a split-type sensorhaving a planar form as shown in FIG. 3 and movable to the left andright by a drive shaft 81 a.

The drive shaft 81 a has a screw thread formed on the outer peripheralsurface thereof serving as a feed screw which makes a screwingengagement with the body of the PD. The drive shaft 85 has a reductiongear mechanism 85 and a potentiometer 87. The arrangement is such thatthe forward and backward rotation of the shaft of the motor 95 istransmitted to the drive shaft 81 a through the reduction gear mechanism85, so that the body of the PD is moved to the left and right as viewedon FIG. 2 (FIG. 3).

The position detecting sensor or the split-type photo-diode has adetecting region which extends in the longitudinal direction thereof,i.e., horizontally, as viewed on FIG. 3. The position detecting sensoris divided into two sections: namely, a section which has a photo-diodedisposed on the right side of the center of the sensor shown in FIG. 3(this photo-diode will be referred to as “right photo-diode”,hereinafter) and a section which has a photo-diode disposed on the leftside of the center of the sensor (this photo-diode will be referred toas “left photo-diode”). Each of the left and right photo-diodes has anoutput terminal. (The output terminal of the right photo-diode will bereferred to as a “right output terminal”, while the output terminal ofthe left photo-diode will be referred to as a “left output terminal”.Both terminals are not shown. Thus, the position detector sensor used inthis embodiment has the form of a split photo-diode which produces atits left and right output terminals positive voltages which are used asthe light detection signals.

More specifically, referring to FIG. 3, when the beam spot of thefocusing laser light impinging upon the position detecting sensorthrough the mirror 65 is formed at a position f₃ which belongs to thedetection region of the right photo-diode, a comparatively high positivevoltage signal is obtained at the right photo-diode, while acomparatively low positive voltage is delivered from the left outputterminal. If the beam spot is formed at a position f₄ which is on theright side of the above-mentioned position f₃, a positive voltage whichis higher than that obtained when the beam spot is at the position f₃ isdelivered from the right output terminal, whereas the left outputterminal delivers a positive voltage which is lower than that obtainedwhen the beam spot is at the position f₃.

Conversely, when the beam spot is located at a position f₂ which iswithin the detection region of the left photo-diode, the relationshipbetween the voltage signals from the left and right output terminals isreverse to that obtained when the beam spot is at the position f₃.Similarly, when the beam spot is at a position f₁ which is on the leftside of the position f₂, the relationship between the voltage signalsfrom the left and right output terminals is reverse to that obtainedwhen the beam spot is at the position f₄.

When the beam spot is located at the central position f₀ on the PD 81shown in FIG. 3, positive voltages of the same level are obtained at theleft and right output terminals. The central position f₀ is a positionwhich may correspond to the optimum focusing condition, i.e., the justfocusing state of the recording lens 77 a, depending on the position ofthe PD 81 relative to the optical base, whereas other positions offsetfrom the center such as f₁, f₂, f₃ and f₄ may correspond to defocusstates of the recording lens 77 depending on the position of the PD 81relative to the optical base. Thus, when the beam spot is located at aposition such as one of f₁ to f₄ which is offset from the centralposition f₀, the position of the recording lens 77 a is automaticallyadjusted by the focus servo circuit 103 and the VCM 77 b, such that thebeam spot impinges upon the central position of shown in FIG. 3,regardless of the position of the PD 81 relative to the optical base.Obviously, the positive voltage signals delivered from the left andright output terminals may be substituted by negative voltage signals .

The light detection signals from the left and right output terminals ofthe above-mentioned split photo-diode are delivered to a differentialamplifier 103 a of the focus servo circuit 103.

Referring back to FIG. 2, a multi-rotation potentiometer which convertsrotation angle to a voltage is used as the potentiometer 87. Themulti-rotation potentiometer detects the amount of rotation of the driveshaft 81 and delivers a voltage signal corresponding to the rotationamount to the amplifier 89. The amplifier 89 amplifies the voltagesignal from the potentiometer 87 at a predetermined amplification factorand delivers the amplified voltage signal to the A/D converter 91. TheA/D converter 91 converts the voltage signal (analog signal) to adigital signal and delivers the digital signal to the digital displayunit 93.

The digital display unit 93 has a plurality of display places each beingcomposed of seven segments. The segments of each place are selectivelydriven in accordance with the digital information given by the A/Dconverter 91, so as to be displayed as numerical information.

The numerical information represents the distance between the instantposition of the PD 81 relative to the optical base during the operationof the VCM 77 b for setting the recording lens 77 a to the optimumfocusing position with respect to the rotating resist master disk 110from a reference position of the PD 81. The reference position of the PD81 is, for example, the position taken by the PD 81 when the head 77 hasbeen set to its optimum position with respect to the resist master disk110 while the disk 110 is not rotating. The numerical information variesdepending on the type of the resist master disk 110 which is to besubjected to the cutting, and is used as the initial value to be set bythe apparatus of the invention for each type of the resist master disk.The manner of the initial setting will be described later in detail.

The motor 95 is a reversible motor which can rotate both forward andbackward, and is driven by the motor driver circuit 97. The focus fineadjust circuit 99 performs fine focusing control of the recording lens77 a by finely moving the PD 81 to the left and right as viewed in FIG.2 or FIG. 3, through the operation of the focus servo circuit 103 andthe VCM 77 b. To this end, the focus fine adjust circuit 99 supplies themotor driver circuit 97 with a control signal for effecting an inchingor fine driving of the motor 95. The focus fine adjust circuit 99 has anoperating portion (not shown) which enables the operator to set theamount of leftward or rightward movement of the PD 81.

The head slider control circuit 101 is a component which is activatedprior to operation of other components, for commencing the initialsetting of the optimum focusing position for each type of the resistmaster disk, or for commencing the focusing operation of the apparatusof the invention (shown in FIG. 2) for the purpose of exposing theresist master disk 110. More specifically, the head slider controlcircuit 101 controls, when the resist master disk 110 is not rotating,the head slider 75 by making reference to an error signal (describedlater) which is generated by an error signal generating means such asthe differential amplifier 103 based on the light detection signalderived from the PD 81 which has been located at a predeterminedposition on the optical base. As a result of this control, the head 77is lowered to a predetermined optimum position from the home position (aposition which is approximately 30 mm above the surface of the resistmaster disk 110).

As described before, the focus servo circuit 103 incorporates thedifferential amplifier 103 a, and is started automatically or by amanual operation of the operator, after completion of the setting of thehead 77 to its optimum position performed by the head slider controlcircuit 101. During the rotation of the resist master disk 110, thefocus servo circuit 103 performs fine adjustment of the position of therecording disk 77 a by controlling the VCM 77 b based on the lightdetection signal derived from the PD 81 which has ben adjusted leftwardor rightward by the operation of the focus fine adjust circuit 99.

This operation will be described more specifically. It is assumed herethat the PD 81 has been located at a certain position on the opticalbase. The differential amplifier 103 a produces a positive or negativevoltage difference (error signal) based on the difference between thevoltages derived from the aforesaid two output terminals. A positivesign of the voltage difference means that the beam spot of the focusinglaser light is located within the detection region of the rightphoto-diode of the PD 81, i.e., a position such as f₃ or f₄ shown inFIG. 3. In such a case, the focus servo circuit 103 performs such acontrol as to move the recording lens 77 a up or down by an amount ofseveral μm, through the operation of the VCM 77 b, until theabove-mentioned voltage difference is reduced to 0 (zero), therebybringing the beam spot to the position f₀. Conversely, a negative signof the voltage difference between the voltage signals derived from thetwo output terminals means that the beam spot of the focusing laserlight is located within the detection region of the left photo-diode ofthe PD 81, i.e., a position such as f₁ or f₂ shown in FIG. 3. In thiscase also, the focus servo circuit 103 performs such a control as tomove the recording lens 77 a up or down, through the operation of theVCM 77 b, thereby bringing the beam spot to, for example, the positionf₀ shown in FIG. 3.

As a consequence, the position of the recording lens 77 a isautomatically controlled such that the beam spot of the focusing laserlight is located on the central position f₀ on the PD 81, even when thebeam spot has been offset to a position such as f₁, f₂, f₃ or f₄ as aresult of setting of the PD 81 at a position after a minute movement ofthe same from the aforementioned certain position.

It is assumed, by way of example, that the head 77 has been set to aposition as shown in FIG. 5 by the operation of the head slider controlcircuit 101, while the PD 81 has been set such that its center islocated at a position S′ shown in FIG. 5. It is also assumed that theposition of the exposure surface of the resist master disk has beenshifted to a position indicated by 110 b due to waving of the resistmaster disk 110 which is rotating. In such a case, the beam 70 of thefocusing laser is reflected by the exposure surface which is indicatedby 72 and is guided to the PD 81 in the manner shown by the numeral 74.Therefore, the cutting is performed by the recording laser light 78while the latter is in a defocus state.

In this case, the focus servo circuit 103 performs a fine adjustmentsuch that the recording lens 7 a is moved away from the resist masterdisk 110, on condition that the position of the PD 81 is reset such thatits center is located at the position indicated by S. Consequently, theposition of the exposure surface of the resist master disk 110 relativeto the recording lens 77 a is changed from the position 110 b to aposition indicated by 110 a. As a result, the beam 70 of the focusinglaser light is reflected by the exposure surface denoted by 80 andimpinges upon the PD 81, whereby the cutting is performed by therecording laser light 78 which is in the “just focus” state, i.e., withthe recording lens 77 a located at the optimum focusing position. Thepotentiometer 87 detects the amount of the displacement of the PD 81from the position where the center of the PD 81 is located at theposition S′ to the position where the center of the PD 81 is located atthe position S. According to a major feature of this embodiment, thedisplacement amount detected by the potentiometer 87 is displayed in theform of digital data.

Obviously, there may be a type of resist master disk with which theoptimum focusing position of the recording lens 77 a is located at theposition indicated by 110 b.

A description will now be given of the focusing process for initiallysetting the optimum focusing position of the recording lens 77 a, withreference to the flowchart shown in FIG. 4.

The process which will now be described uses focusing position datawhich are deemed to be optimum focusing position data which have beenacquired through a manual operation executed by a skilled operator.(Such focusing position data will be referred to as “predicted optimumfocusing position data”.)

At the beginning of the focusing process, the operator locates the PD 81at a predetermined position on the optical base. Then, the focusinglaser 73 is started, while the resist master disk 110 is kept fromrotating. Then, driving instructions are given to the head slidercontrol circuit 101 which in turn controls the head slider 75 so as tolower the head 77 (Step S121). During this operation, the head slidercontrol circuit 101 periodically and cyclically checks whether or notthe head has reached a predetermined optimum position, by makingreference to an error signal derived from, for example, the differentialamplifier 103 a (Step S122).

When the result of the periodical check shows that the head 77 is stillabove the optimum position (Step S123), the downward movement of thehead 77 is continued (Step S121), whereas, when the result shows thatthe head 77 has come down below the optimum position (Step S123), thehead slider control circuit 101 terminates the downward motion of thehead 77 and, instead, commences upward movement of the head 77 (StepS124). It is to be noted that the operator is prohibited from startingthe focus servo circuit 103 during execution of the above-describedcontrol operation performed by the head slider control circuit 101. Whenit is judged that the head 77 has reached the above-mentioned optimumposition (Step S122), the head slider control circuit 101 terminates thedriving of the head slider 75 (Step S125).

The focus servo circuit 103 is started (Step S126) when it is determinedafter the start of rotation of the resist master disk 110 that theabove-mentioned optimum position of the head 77 cannot locate therecording lens 77 a at the optimum focusing position. The operator thensets, through the operating portion of the focus fine adjust circuit 99,an amount of fine movement of PD which corresponds to the aforesaidpredicted optimum focusing position data, so that the focus fine adjustcircuit 99 finely drives the PD 81 to the left or right (Step S127). Thedifference between the voltage signals derived from the two outputterminals of the PD 81 varies partly because of a waving of the disksurface due to rotation of the resist master disk 110 and partly becauseof the above-described fine movement of the PD 81. In order tocompensate for this variation, the focus servo circuit 103 causes therecording lens 77 a to move up or down by an amount of several μm, so asto reduce the voltage difference to 0 (zero). It is possible that therelative position of the recording lens 77 a in the head 77, as obtainedafter the above-described adjustment for reducing the voltage differenceto 0, is the optimum focusing position under rotation of the resistmaster disk 110. The operator then compares the numerical informationdisplayed on the digital display unit 93 with the above-mentionedpredicted optimum focusing position data (Step S128). If the displayednumerical information coincides with the predicted optimum focusingposition data, the predicted optimum focusing data is held as being theoptimum focusing data (Step S129) and is used as the data for initialsetting of the optimum focusing position (Step S130).

Conversely, if the comparison conducted in Step S128 has proved that thedisplayed numerical data does not coincide with the predicted optimumfocusing position data, the predicted optimum focusing position data isupdated by being substituted by the displayed numerical information(Step S131). The process then proceeds to Step S130.

By repeating several times the operation of the steps S121 to S131, itis possible to acquire optimum focusing position data for each of thedifferent types of resist master disks.

Thus, in the described embodiment of the invention, optimum focusingposition data corresponding to the type of the resist master disk 110 tobe processed is selected prior to the exposure of the resist master disk110, and the optimum focusing position of the recording lens 77 a isinitially set based on the selected optimum focusing position data,whereby the variation of shapes of the bits or grooves formed in thereplicated disk can be reduced as compared with the known arts.

A description will now be given of the result of a comparison betweenthe variation of the relationship between the depth and width of thebits (or grooves) formed in a disk replicated from the resist masterdisk prepared in accordance with the described embodiment and thevariation of the relationship between the depth and width of the bits(or grooves) formed in another disk replicated from a resist master diskprepared in accordance with a known technique.

FIG. 6 shows the variation of the relationship between the depth andwidth of the bits (or grooves) formed in a disk replicated from theresist master disk 110 prepared in accordance with the describedembodiment, while FIG. 7 shows the variation of the relationship betweenthe depth and width of the bits (or grooves) formed in a disk replicatedfrom the resist master disk prepared in accordance with the knowntechnique.

In each of FIGS. 6 and 7, axis of ordinate represents the width, whileabscissa represents the depth, of the bits (or grooves). A certainrelationship exists between the depth and width of bits (or grooves):namely, the greater the depth, the greater the width. This constantrelationship is maintained only when the fluctuation of the focusingposition of the recording lens 77 a is small. Thus, the relationship isvaried when the focusing position of the recording lens 77 a fluctuates.

FIG. 6 shows the variation of the relationship obtained in a case wherethe fluctuation of the focusing position of the recording lens 77 a issmall, while FIG. 7 shows the variation observed when the fluctuation ofthe focusing position of the recording lens 77 a is significant. Acomparison between the data shown in FIG. 6 and those shown in FIG. 7clearly demonstrates that the variation of the relationship between thedepth and width of the bits (grooves) is smaller in the disk replicatedfrom the resist master disk 110 prepared in accordance with theembodiment than in the disk replicated from the master disk prepared inaccordance with the known technique.

FIG. 8 is a block diagram showing the whole structure of a recordingapparatus in accordance with a second embodiment of the presentinvention.

As will be seen from this Figure, the recording apparatus of the secondembodiment differs from the recording apparatus of the first embodimentin that the former has an optimum focusing position confirming circuit105 and a manually operable switch 107 which are connected between theoutput of the amplifier 89 and the input of the focus servo circuit 103.

Other features of the second embodiment are the same as or similar tothose of the first embodiment and, therefore, are not described to avoidduplication of explanation.

The optimum focusing position confirming circuit 105 has a functionsubstantially equivalent to the operating portion of the focus fineadjust circuit 99 employed in the first embodiment, and is used in theoperation for the initial setting of the optimum focusing position. Theoptimum focusing position confirming circuit 105 has, as shown in FIG.9, a differential amplifier 105 a, a reference voltage setting circuit105 c connected to the inversion input terminal of the differentialamplifier 105 a, and an amplifier 105 b having a buffering function.

A variable resistance circuit capable of dividing a voltage into desiredvoltages is used as the reference voltage setting circuit 105 c. Morespecifically, the reference voltage setting circuit 105 c has a sliderwhich is operable by the operator, thus enabling the operator to set areference voltage corresponding to the amount of fine movement of the PD81 indicative of the predicted optimum focusing position data.

The differential amplifier 105 a computes the difference between theoutput signal derived from the amplifier 89 and the reference voltageapplied by the reference voltage setting circuit 105 c, and produces avoltage signal (error signal) corresponding to the voltage difference.The error signal is delivered to the focus fine adjust circuit 99 onlywhen the switch 107 has been closed. The focus fine adjust circuit 99,upon receipt of the error signal, controls the motor 95 through theoperation of the motor drive circuit 97, thus effecting a fine movementof the PD 81 to the left or right.

The switch 107 is manually closed by the operator only when the initialsetting of the optimum focusing position is conducted by means of theoptimum focusing position confirming circuit 105. This switch 107,therefore, is opened once the initial setting of the optimum focusingposition is completed.

FIG. 10 is a flowchart showing the focusing process conducted for thepurpose of initial setting of the optimum focusing position of therecording lens 77 a in the recording apparatus of the second embodiment.This process is discriminated from the process of FIG. 4 only by theoperation performed in Step S127 and the operation performed in StepS123, as will readily be seen from the comparison between the flowcharts of FIGS. 4 and 10.

More specifically, referring to FIG. 10, the focus servo circuit 103 isstarted (Step S126) and then a reference voltage corresponding to thepredicted optimum focusing position data is set by the reference voltagesetting circuit 105 c (Step S132) while the switch 107 is kept open.Then, the switch 107 is closed, so that the motor 95 is controlled inaccordance with the signal which indicates the difference between theoutput signal from the amplifier 89 and the reference voltage and whichis computed by the differential amplifier 105 a, whereby the PD 81 isfinely moved to the left or right. Thereafter, operations describedbefore are executed including the adjusting operation for adjusting therecording lens 77 a up or down by the amount of several μm performed bythe focus servo circuit 103, as well as the checking executed by theoperator as to whether the optimum focusing position has been reached.

The apparatus of the second embodiment offers substantially the sameadvantages as those of the apparatus of the first embodiment.

Although the invention has been described through illustration ofspecific embodiments, it will be understood that the describedembodiments are not intended to limit the scope of the presentinvention.

As has been described, the present invention provides a recordingapparatus which permits easy initial setting of the optimum focusingposition suitable for the type of the resist master disk to beprocessed, by virtue of the feature that the data indicative of theoptimum focusing position of the recording lens is handled in the formof numerical values.

INDUSTRIAL APPLICABILITY

The recording apparatus of the present invention can suitably be used asa laser cutting machine.

What is claimed is:
 1. A recording apparatus for exposing a resistmaster disk to a recording laser light through a recording lens whichhas been set at an optimum focusing position, comprising: displaceablelaser light detector for receiving a focusing laser light which has beenapplied to and reflected from said resist master disk during initialsetting of the optimum focusing position, and for producing a detectionsignal indicative of an amount of deviation, from a predetermined lightreceiving position, of a light receiving position where a reflectedfocusing laser light is received; a servo responsive to said detectionsignal so as to automatically adjust a relative position of saidrecording lens with respect to said resist master disk in such a manneras to eliminate said deviation, thereby setting the recording lens atthe optimum focusing position; displacement amount detector fordetecting an amount of displacement of said laser light detector; and adisplay for changing an output from said displacement amount detectorinto numerical values and displaying the numerical values.
 2. Arecording apparatus according to claim 1, further comprising: referencedisplacement amount setter in which a reference displacement amount hasbeen set in terms of an amount of displacement required to obtaincoincidence between said light receiving position at which the focusinglaser light is received and said reference light receiving positionunder such a condition that said recording lens has been set at theoptimum focusing position; and automatic displacement amount adjustorfor automatically adjusting the amount of displacement of said laserlight detector such that a detection output from said displacementamount detector coincides with said reference displacement amount.
 3. Arecording apparatus comprising: a recording lens for focusing laserlight; a resist master disk disposed proximate the recording lens toreceive and reflect the laser light; a displaceable laser light detectordisposed proximate the resist master disk to receive the laser lightreflected therefrom, the displaceable laser light detector generating amotion signal corresponding to an amount of deviation of the laser lightfrom a pre-selected position; and a servo coupled to the recording lensand communicating with the displaceable laser light detector, the servoautomatically adjusting a position of the recording lens relative to theresist master disk in response to the motion signal from thedisplaceable laser light detector so as to achieve an optimum focusingposition.
 4. The apparatus of claim 3 further comprising: a displacementdetector communicating with said displaceable laser light detector andgenerating a displacement output corresponding to a magnitude of thesignal generated thereby.
 5. The apparatus of claim 4 furthercomprising: a display communicating with the displacement detector anddisplaying numerical values corresponding to the displacement output. 6.The apparatus of claim 3 further comprising: a reference displacementamount setter that sets a reference displacement amount and communicatesthe displacement amount to the displaceable laser light detector using adisplacement signal which is transmitted to the servo which moves therecording lens to an optimum focusing position.
 7. The apparatus ofclaim 6 further comprising: an automatic displacement amount adjustor toautomatically adjust the displaceable laser light detector so that adisplacement output from the displacement laser light detector coincideswith the reference displacement amount from the reference displacementamount setter so that a displacement signal is transmitted to the servoto adjust the recording lens to achieve an optimum focusing position.